: 1970 deville rear axle and drive shaft

12-13-10, 06:11 PM
Im looking to upgrade my driveshaft but am unsure of a few things:
Is this a 3.5" diameter shaft? If not then what dimension?
And what axle did this come with, if it varies how can I find out?
Thank you very much

Im looking to upgrade the driveshaft now and replace the rear axle with a 12 bolt gm eventually so I was hoping it would fit within both.
Thanks again!

12-13-10, 06:15 PM
The rear in your Cadillac is already as strong as a 12 bolt. No need to change it. No idea of the diameter of your shaft, but if you are looking to upgrade, call Denny's.

12-13-10, 06:34 PM
What motor/tranny combo do you plan on using?

12-13-10, 07:09 PM
It funny... I was just talking to a guy trying to find a drive shaft for a '71; said they cost $500-$1,000.

12-13-10, 07:42 PM
No idea of the diameter of your shaft, but if you are looking to upgrade, call Denny's.

that's what she said... :yup:

12-13-10, 07:46 PM
^I don't think that work out the same way as you intended...

12-14-10, 08:14 AM
What motor/tranny combo do you plan on using?

Its a twin turbo oldsmobile 455 with a turbo 400, about 650 horsepower. and Dennys was the place I asked! Is it really pretty close to those eaton rear axles with a posi that go for about 2k-3k?? So maybe its worth rebuilding with a posi instead?

12-14-10, 09:15 PM
I dunno if you're looked things over very closely, but here's my humble opinion:
You are asking for a LOT of work that you have not foreseen. The Cadillac rear end has a very special build to allow the driveshaft to ride very low in the car. Too, the tunnel is very low in the car. The engine also has a bit more rake to achieve the same end.

Now, if you simply swap in a 12 bolt, you will lose:
The rear CV joint, as it is a flange-mount.
The special low entry of the pinion.
This will cause:
You will now need a custom driveshaft, as you can no longer utilise the CV joints. You will then need to raise the shaft in the car to keep the U-joints in phase and in line.
You will also need to raise the driveshaft tunnel, for the above reasons. This will affect the entire interior, as the seats are not designed for a high tunnel, which you now need.
Not to mention that most 12 bolt rears do not come with enough brake for this car, so you'll need truck brakes.


12-15-10, 04:34 AM
Ok thank you very much! If I were to get Danny's driveshaft for the stock rear axle what type of axle do I tell him? And are there any specifications out there (ex. drive shaft length & diameter) so that when I order it, that it will bolt right up? And what type of pinion yoke would I need?
Thanks alot everyone! i plan to order this soon so it would be very helpful

12-15-10, 02:15 PM
Denny's will give you a sheet you fill out with all the specs and measurements. It is on their website.

Just use your stock shaft until you get your engine installed and running ;)